Sampling aerosol particles from high-speed flows is modeled with the help of numerical solution of the Navier-Stokes equations. The effect of a coaxial shield mounted around the inlet tube of a sampler and the width of tube walls on aspiration distortions of the aerosol size spectrum is studied. Based on the calculated results, a device for sampling aerosol particles and separating them into two fractions has been designed. The obtained results can be used in the development of samplers for airborne studies of atmospheric aerosols.